The present invention relates to an intervertebral disk stabilizing implant and a method of stabilizing two adjacent vertebrae. More specifically, the present invention relates to upper and lower interlocking brackets which attach to adjacent vertebrae sufficiently to stabilize the vertebrae but allow for some forward flexion and rearward extension of the spine with slight lateral displacement. An alternative embodiment provides for stability of the spinal column, with flexion and extension with spinal shock absorption.
The spine is a flexible structure comprised of thirty-three vertebrae. The vertebrae are separated and cushioned from each other by fibrous cartilage in structures called intervertebral disks. If the spine is injured or becomes diseased, surgical intervention involving removal of one or more of these disks and fusion of the adjacent vertebrae, may be indicated. Such disk injuries can happen in the neck, in the thoracic region and in the lumbar region. The more frequent injuries are in the lower lumbar and in the lower cervical regions.
Treatment of a herniated disk in the neck and in the lumbar region continues to be a challenging field of medicine. The classical treatment for a ruptured disk continues to be removal of the disk from between the vertebrae. By this process of removing the disk, overall spinal instability is increased. This may aggravate the patient to some degree after the operation. Another procedure previously employed is to replace the disk space with a bone graft, bringing about fusion of the vertebrae above and below the disk, eliminating the empty space between the vertebrae and improving stability.
Theoretically a diskectomy with fusion is a satisfactory procedure, though not ideal because the replaced bone does not have the principal functions of the cartilage tissue of the disk. This fusion procedure is technically demanding and has medical complications because of several physiological factors.
It must be remembered that the disk primarily serves as a mechanical cushion while permitting limited mobility. For any replacement system for a disk to be truly effective, it must allow for mobility within the natural limits of the original disk. In other words, the replacement should match appropriate joint rheology (movement behavior). The natural disk allows about 11 degrees of flexion-extension, limited lateral bending of 3 to 5 degrees, and very restricted rotation of about 1 degree.
Various prosthetic devices and implants are disclosed in the art, but all are characterized by compromises to the full functions of a natural disk discussed above. Examples of the prior art include the following U.S. Pat. Nos. 5,893,890; 5,693,100; 5,658,336; 5,653,761; 5,653,762; 5,390,683; 5,171,278; and 5,123,926. The present invention improves upon the state of the art including the inventor's own prior inventions by more closely approximating the natural function of the disk, including extension-flexion, slight lateral bending, and very slight rotation.